1. Field of the Invention
This invention relates generally to cooling and heating systems, and more particularly to a combined heating and cooling system utilizing the thermodynamic properties of air. While the present invention may be utilized to control the climate in any area it is particularly contemplated for use in driver's cabins in locomotives and the like rooms.
2. Description of the Related Art
Currently, the most popular cooling systems are based upon vapor compression processes, such as the Carnot cycle. As is well known, in a device operating in accordance with a vapor-compression refrigeration cycle, a working fluid such as FREON enters a compressor as a slightly superheated vapor at low pressure. It then leaves the compressor and enters a condenser as a vapor at some elevated pressure, where the working fluid is condensed as a result of heat transfer to cooling water or to the surroundings. The refrigerant then leaves the condenser as a high pressure liquid. The pressure of the liquid is decreased as it flows through an expansion valve, and, as a result, some of the liquid flashes into vapor. The remaining liquid, now at low pressure is vaporized in the evaporator as a result of heat transfer from the cooled spaced.
Increasing research has been directed toward alternatives to systems of the above type because they often utilize a working fluid containing chlorofluorocarbons (CFC's), such as FREON, which has been identified as a cause of ozone layer thinning and a contributor to the greenhouse effect. One such system utilizes the thermodynamic properties of air and is based on the Joule process or air-standard refrigeration cycle. In comparison to vapor-compression systems, there is generally a significantly higher energy requirement so that their application remains limited to airplanes and certain other special situations. Increasing use of air-standard cycle systems now appears likely, however, because it does not utilize the environmentally damaging coolants associated with vapor compression systems Since the energy consumed by the the system is directly proportional to the indirect greenhouse potential (due to the expenditure of fossil fuels), an air-standard cycle system must be designed so as to be at least equivalent to vapor-compression systems and electrical heating devices in terms of their environmental impact.
Since temperatures above the ambient temperature also occur in an air-standard cycle process, configurations have been proposed which provide for the simultaneous or alternative use of the process for heating and cooling so that significantly improved efficiencies and energy ratios can be achieved. Such configurations typically include two-stage compression in two separate compressors. The compressor of the first stage is driven by an electric motor and that of the second stage by the expansion or flash turbine. During the cooling process, a closed primary circuit of the air with intermediate cooling and regenerative heat exchange between the compressor of the second stage and the flash turbine is realized. The air of the secondary circuit is cooled in a load-heat exchanger downstream of the flash turbine and is then fed to the room to be cooled. An arrangement of reversing valves and bypass lines forms an open primary circuit which succeeds in feeding the warm air occurring downstream of the compressor to the load-heat exchanger so that the secondary circuit can be used to heat the room.
The advantage of the two stage compression configuration described above is that it achieves a considerable reduction in the average annual energy consumption and an improved efficiency of the system in comparison to the heating of railroad passenger coaches by electric resistance heating elements and cooling by means of vapor-compression systems. The principal disadvantage of the system, however, is its high capital cost necessitated by the need for two compressor stages, the heat exchanger for the secondary circuit, the reversing valves, and the bypass lines. Accordingly, this energy-saving construction would not be economically feasible for smaller rooms, such as the driver's cabins in locomotives or service quarters of passenger coaches.
It is therefore an object of the present invention to provide a heating and cooling system utilizing an air-standard cycle apparatus which is highly efficient when compared to vapor-compression devices and which is economical to construct and operate, even for processing the air of small rooms.